This invention relates to a process for the purification of hexafluoro-1,3-butadiene, and more particularly to such a process employing an adsorbent to accomplish the desired purification.
Hexafluoro-1,3-butadiene (HFBD) is employed in the manufacture of semiconductors as an etchant for silicon oxide and related materials. HFBD employed in the semiconductor industry must be of extremely high purity. Commercially available HFBD is of 99.0 to 99.9 vol % purity, and contains a mixture of partially fluorinated and chlorinated isomers of butadiene, butadiene dimers, starting materials and solvents. The semiconductor industry requires HFBD of greater purity.
It is known to use adsorbents to remove perfluorinated olefinic impurities from perfluorinated, saturated compounds. For example, U.S. Pat. No. 3,696,156 discloses a process comprising the use of alumina for vapor phase removal of olefinic impurities from saturated fluoroperhalocarbons. The process is conducted in a temperature range from 180xc2x0 C. to 250xc2x0 C.
U.S. Pat. No. 5,300,714 and related patent documents U.S. Pat. No. 5,507,941 and EP 0457613B1 teach the removal of olefinic impurities from a saturated fluoroperhalocarbon liquid by contacting the liquid with alumina-type compounds at ambient temperatures. The use of 5 xc3x85 molecular sieve is disclosed; however, it exhibited the lowest efficiency for removing pefluoroisobutylene from perfluorinated alkane (33%) of any adsorbent shown in Table 3 of the ""714 patent, other than the comparative example adsorbents. Liquid contact and temperatures above room temperature were required and no preferential removal of one olefinic impurity over another was reported. No mention was made of removing moisture, HF and/or iso-propyl alcohol, which are impurities specific to HFBD.
JP 10287595 discloses the use of adsorbents to remove C2 hydrofluorocarbon impurities (C2HFCs) from the saturated compound hexafluoroethane. Suitable adsorbents include zeolites having an average pore diameter of 3.5-11 Angstroms and a silica/alumina ratio less than or equal to 2.0; and carbonaceous adsorbents having an average pore diameter of 3.5-11 Angstroms. The adsorbents are said to be able to reduce C2HFCs in hexafluoroethane to 10 ppm or less.
As for the purification of unsaturated compounds containing fluorine, U.S. Pat. No. 3,381,041 discloses the use of sulfuric acid and mercurial type compounds from 0 to 150xc2x0 to remove olefinic impurities from saturated and unsaturated hydrofluorocarbons. However, there is no disclosure of using an adsorbent, such as a zeolite, to remove the impurities.
Despite the foregoing developments, it is desired to provide a process for purifying HFBD to a purity greater than 99.99%. It is further desired to provide such a process based on the use of an adsorbent to remove impurities. It is still further desired to provide a process for removing hydrofluorocarbon impurities and non-hydrofluorocarbon impurities, such as water, HF and/or alcohol(s), from HFBD to provide HFBD containing less than 0.01% of such impurities.
All references cited herein are incorporated herein by reference in their entireties.
Accordingly, the invention provides a process for purifying HFBD, which process comprises: (a) contacting a composition containing said HFBD with an adsorbent to remove from said HFBD at least two impurities selected from the group consisting of water, an alcohol, hydrofluoric acid and a fluorinated olefin, wherein said adsorbent is a solid having an average pore diameter of about 5 xc3x85 and said adsorbent is contacted with said HFBD at a rate of at least 2.7 kg of said HFBD per hour; and (b) recovering from said adsorbent a purified HFBD product containing at least 99.9 vol. % HFBD, a reduced amount of said impurities and less than 0.1 vol. % hexafluoro-2-butyne.
Also provided is a process comprising: (a) contacting a composition containing said HFBD with an adsorbent to remove from said HFBD at least two impurities selected from the group consisting of water, an alcohol, hydrofluoric acid and a fluorinated olefin, wherein said adsorbent is a solid having an average pore diameter of about 5 xc3x85; and (b) recovering from said adsorbent a purified HFBD product containing more than 99.96 vol. % HFBD, a reduced amount of said impurities and less than 0.04 vol. % hexafluoro-2-butyne.
Still further provided is a process comprising: (a) contacting a composition containing said HFBD with an adsorbent to remove from said HFBD at least two impurities selected from the group consisting of water, an alcohol, hydrofluoric acid and a fluorinated olefin, wherein said adsorbent is a solid provided as a bed within a column having a length of at least 30 cm and an inner diameter of at least 2.5 cm, and said contacting comprises passing a feed gas containing said HFBD over said bed; and (b) recovering from said adsorbent a purified HFBD product containing at least 99.9 vol. % HFBD, a reduced amount of said impurities and less than 0.1 vol. % hexafluoro-2-butyne.
Additionally provided is a process comprising: (a) contacting a composition containing said HFBD with an adsorbent to remove from said HFBD at least two impurities selected from the group consisting of water, an alcohol, hydrofluoric acid and a fluorinated olefin, wherein said adsorbent is a solid having an average pore diameter of about 5 xc3x85; (b) recovering from said adsorbent a purified HFBD product containing more than 99.9 vol. % HFBD, a reduced amount of said impurities and less than 0.1 vol. % hexafluoro-2-butyne; and (c) reactivating said adsorbent after said adsorbent has been spent by at least one cycle of said contacting and said recovering, wherein said reactivating comprises heating said spent adsorbent under a dry inert gas purge, and then cooling said heated adsorbent to room temperature prior to additional said contacting.
HFBD produced by the process of the invention is also provided.